Since the introduction of a first smartphone in 1994, there has been a rapid growth in smartphones' technology. Smartphones have become much more than just computers; they also provide functionalities of personal databases, jukeboxes, cameras, communications hubs and communications gateways.
As today's smartphones are increasingly used to store and communicate sensitive financial and personal information, a reliable assessment of an identity of the smartphone's user is emerging as an important new service. Personal identification numbers or passwords appear to be insufficient for this purpose.